Apparatus for producing x-ray images as radiographs

ABSTRACT

This invention relates to the novel system of radiography. The image of examined object is formed by X-radiation. This image is converted in a vacuum tube into a beam of electrons. The beam of electrons is converted next into an electrical pattern and is stored on a movable sheet of dielectric material which travels through said vacuum tube. Means are provided for feeding said sheet or tape of dielectric material into said vacuum tube and for transporting it after X-ray exposure to the outside of said vacuum tube. The stored image is next developed, is made visible and is fixed with or without transfer to another medium in order to produce the final visible radiograph for inspection.

United States Patent Sheldon Nov. 25, 1975 [54] APPARATUS FOR PRODUCINGX-RAY 3,453,639 7/1969 Berman 1. 346/110 V IMAGES AS RADIOGRAPHS3,515,870 6/1970 Marquis 1 1 1 u 250/320 2,877,368 3/1959 Sheldon 313/[76] Inventor: Edward Emanuel Sheldon, 30 E. 40

New York NY 0016 Primary Examiner-1ames W. Lawrence [22] Filed: May 16,1973 Assistant Examiner-B. C. Anderson [21] Appli No.: 360,753

ABSTRACT [52] US. Cl. 250/320; 250/483; 250/475 This invention relatesto the novel system of radiogra- [51] Int. Cl. G0ln 23/04 phy. The imageof examined object is formed by X- [58] Field of Search 250/315, 320,321, 323, radiation. This image is converted in a vacuum tube 250/483,475; 346/110 V into a beam of electrons, The beam of electrons isconverted next into an electrical pattern and is stored [56] ReferencesCited on a movable sheet of dielectric material which travels UN|TEDSTATES PATENTS through said vacuum tube Means are provided for 2l984794/1940 Langmuir H 250/320 feeding said sheet or tape of dielec tricmaterial into 2,221,776 H1940 Carlson V p I v I I I 4 H /5 said vacuumtube and for transporting it after X-ray 2,440,640 4/1943 Manon 250/320.exposure to the outside of said vacuum tube. The 155 423 /195 Sheldon29 71 stored image is next developed, is made visible and is 3,021.8342/1962 Sheldon 128/6 fixed with or without transfer to another medium in3,099,710 7/1963 M611er et a1. 346/ V order to produce the final visibleradiograph for in- 3,236,943 2/1966 Mdller 346/110 v spec/ion 3,281,85810/1966 Schwertz 346/110 V 3,400,291 9/1968 Sheldon 1. 313/65 9 Claims,6 Drawing Figures C'AMAG/NG CAM/ I 7 /7 .1- L, 1 5 6 mi l 1 1 /6 WV I 8/5 r VACUUM LOCK 17 0E VELOP/NG S R 0; 04444552 20 P075V774L l4fi7X/A/6' cmswaee 2/ IPEL-L APPARATUS FOR PRODUCING X-RAY IMAGES ASRADIOGRAPHS This invention relates to a novel system of radiographywhich means to the apparatus for producing pictures formed byX-radiation. The present systems are all based on the use of films madewith silver halides and which are used in combination with Xraysensitive fluorescent screens. The present radiographic systems do notprovide any means for intensifiction of the X-ray image and as a resulta large amount of X-radiation is necessary to produce a radiograph. Thismay be not of crucial importance in industrial radiography but is ofgreat importance in the medical radiography in which the X-ray exposureof patients should be kept at minimum. In view of the fact that thenumber of X-ray examinations increases greatly every year, the concernis voiced that many patients, especially of reproductive age receive toolarge amount of X-radiation which may affect their genetic system. Thismeans that the number of congenital malformations in new-born mayincrease greatly. It is therefore of great importance to provide asystem of radiography which will reduce the X-ray exposure of patientsand still will provide the necessary diagnostic information. This is themain objective of the present invention.

Another objective of this invention is to reduce the costs of X-rayexamination. In view of multiple and extensive X-ray examinations whichare necessary in hospital work, the cost of X-ray examinations are veryhigh. The present invention, by eliminating the use of expensive X-rayfilm and substituting them with very cheap plastic materials willgreatly contribute to the reduction of X-ray examination expenses.

Another objective of this invention is to produce X-ray images of betterdiagnostic quality than it was possible using the present methods ofradiography.

The above objectives were realized by the novel system of radiographywhich is characterized by the use of electronic amplification of X-rayimages in a novel vacuum tube and of inexpensive materials such plasticsfor reproducing X-ray images in a visible form as radiographs.

The invention will be better understood when taken together with theaccompanying drawings.

IN THE DRAWINGS FIG. 1 shows the new apparatus for radiography whichcomprises an X-ray sensitive vacuum tube and dielectric film travellingthrough said tube.

FIGS. l-A and 1-]! show modification of the X-ray sensitive screen usedin the vacuum tube illustrated in FIG. I.

FIG. 2 shows a modification of the apparatus for radiography in whichthe X-ray sensitive vacuum tube contains a layer of material whichexhibits electron bombardment induced conductivity, said layer movablethrough said tube.

FIG. Z-A shows a modification of the layer used in the embodiment ofFIG. 2.

FIG. 3 shows a modification of the apparatus for radiography in which afilm comprising a layer of photoconductive material is used in a vacuumtube.

FIG. 1 shows the X-ray source 15, the examined object I6 and the novelX-ray sensitive image tube 1 which comprises an evacuated envelope 2.The X-ray sensitive photocathode or screen 3 may be mounted 2 on theinside surface of the endwall of said tube or it may be mounted in aspaced apart relationship from said endwall. In the latter case it willbe supported by the supporting member 5 such as of aluminum orberyllium. The photo-cathode 3 comprises furthermore fluo rescent layer6 of one of phosphors such as of CsI or ZnSCdS or CaWO, or of mixturethereof and of photoemissive layer 7 such as of CsSB or K-Cs-Sb, Na-KSbor other photo-electric materials of multi-alkali type. The X-ray imageis converted in said photo-cathode 3 into a fluorescent image and nextinto a beam of free photo-electrons corresponding to the X-ray image.The beam of photo-electrons is accelerated to the necessary velocity byelectrostatic electrodes and then is focused by electrostatic ormagnetic focusing means 4 onto electron reactive dielectric film 8. Insome cases as shown in FIG. l-A the focusing electrodes may be omittedand photo-electron or electron beam may be focused onto film 8 byproximity focusing. In such case the spacing between the photo cathode3b and film 8 should not exceed 2mm and the photo-cathode 3h will have aplanar shape. The electron reactive film 8 may be one of flexible orsemi-flexible plastics of a high electrical resistivity such aspolyesters, polyamides,

polyethylenes or polycarbonates. Preferably a transparent materialshould be used but this is not obligatory.

In another embodiment of invention the film 8 comprises a continuous ormosaic layer of material which is a good emitter of secondary electronssuch as MgO or alkali halide which is mounted on the surface of film 8which faces the photo-cathode 3 and receives the photo-electron beam.The impingement of said photoelectron beam will produce secondaryelectron emission which may be collected by a suitable collectorelectode and will leave positive or negative electrical charge on thesurface of said electron emitting layer. The film 8 is mounted to beable to travel into the vacuum tube 1 from the film supply chamber 22which comprises film feeding mechanism. After the exposure by thephoto-electron beam in said vacuum tube film 8 is transported outside ofsaid tube 1 to developing chamber 20. Vacuum safety locks 17 serve forthe entry and exit of film 8.

The film 8 may be of planar shape or may have curvature at the time ofthe exposure to the electron beam. The curvature of film 8 will dependon electronoptics used in vacuum tube I and may be produced by the useof supporting electrode 10 which is provided with the necessarycurvature. The electrode 10 may be connected to the source of potentialand provide the necessary voltage to produce secondary electron emissionfrom the film 8 either higher than unity or lower than unity accordingto the application of this apparatus. The collector electrode forsecondary electrons may be in the form of mesh screen 18. In theembodiment of invention which uses electrostatic focusing means the film8 or its modifications may have a curvature with the concavity facingthe concavity of the photo-emissive layer or it may be also of planarshape. In the embodiment in which magnetic focusing means are used andalso in modification in which the proximity focusing is used, the film 8will have planar shape parallel to the planar shape of thephoto-emissive layer.

The dielectric film 8, in some applications receives in a chargingchamber 19 before its introduction into the X-ray sensitive vacuum tubeI an electrostatic uniform charge of positive sign on its surface whichwill face the photo-cathode 3. The dielectric film 8 positivelyprecharged will be now introduced into vacuum tube 1 and will bebombarded by the photo-electron beam. In this modification the velocityof photo-electron beam must be such that it produces secondary electronemission of less than unity and forms thereby a negative charge image onfilm 8. This negative charge image is immediately neutralized by thepositive electrostatic charge which was deposited on film 8 previously.As a result the remaining positive charge on film 8 will have thepattern of the original photo-electron beam and therefore of theoriginal X-ray image. The film 8 is now transported out of the vacuumtube 1 and travels into developing chamber which may have various formswell known in the art and which may use a toner for said development.The film 8 with the developed image is transported now into transfer andfixation chamber 21 to produce the permanent image. If the transfer ofimage onto another material is desired, it can be done by well-knowntransfer techniques. The final image may he therefore in the form oftransparency and can be examined with transmitted light like anyconventional X-ray film, or it may be in non-transparent form in whichcase it will be examined with reflected light In another modification ofinvention the film 8 is charged uniformly with electrostatic charge ofnegative sign. In this embodiment the photo-electron beam is acceleratedto velocity in which the secondary electron emission is higher thanunity. The secondary electrons are led away by the mesh screen 18. As aresult. the positive charge is formed on film 8 and it is neutralized bythe negative electrostatic charge deposited previously. In this way theremaining negative charge will have the pattern of the originalphoto-electron beam which again had the pattern of the original X-rayimage. The rest of developing and fixing and transfer pro cedures is thesame as was described above.

It should be understood that in many applications film 8 may be usedwithout pre-charging it with electrostatic charge as was describedabove. In such case the electrostatic charge will be applied to film 8in the developing chamber 20.

It was found however that in some applications such as in medicalradiography where the imaging X-radiation has to be very low in ordernot to harm patients, the above described devices do not have thesensitivity which is necessary. It was found that in examinations ofheavy parts of patients such as abdomen, it is necessary to improve thesensitivity by a factor of 100-200. In order to obtain such improvement,it is necessary to increase the current density of the photo-electronbeam without increasing the amount of X-radiation. This was accomplishedby using cascade intensification in which another composite screen madeof a light reflecting layer, a fluorescent layer, a light transparentsupporting member and of a photo-emissive layer in that order is mountedin spaced relation to the photo-cathode 3. The photo-electron beam fromphoto-cathode 3 is accelerated to 15-20 KV before it impinges on thesecond composite screen producing thereby intensification ofphoto-electron beam by a factor of 50-100 as it was described in my U.S.Pat, No. 2,555,423. It may be added that the supporting lighttransparent layer for the second composite screen may be of vacuumresistant plastic material such as polyamide or silicone in order to beable to make this second composite screen of size necessary in medicalradiography. In some cases the fluorescent layer may be mixed with alight transparent 4 separating layer to make a self-supporting member ofthis mixture.

This construction will give intensification by factor which will bestill insufficient for Xray examinations of heavy parts. The sensitivityshould be improved by an additional factor of 2 to 3. This wasaccomplished by coating the surface of dielectric film 8 which isexposed to the primary beam of photo-electrons or electrons from theX-ray reactive screen 3 with a layer of good secondary electron emittersuch as MgO or an alkali halide. A good secondary electron emitter meansmaterial which emits more of secondary electrons than the dielectricfilm 8. For example, secondary electron emission of plastics is limitedto 2 secondary electrons for one primary electron, whereas MgO will emit4-5 secondary electrons for one primary electron. The layer of goodelectron emitter may be a continuous layer if the said material isinsulator or should be ofmosaic type if said material is ofsemi-conducting or conducting type.

Another way to amplify the photo-electron beam is to use a multi-channelmultiplier as described in my U.S. I-atv No. 3,400,291.

Another way to amplify the photo-electron beam is by the use of anelectron multiplier oftransmission type such as a membrane of siliconpreferably of p-type.

All these amplifying means will increase the sensitiv ity of thisapparatus for radiography by a factor of IOU-2000. The above describedamplification allows to use the very low sensitivity dielectric film 8without increasing the amount of X-radiation and such combinationrepresents an important feature of this invention.

In all embodiments of invention it is advantageous for bettersensitivity to demagnify the photo-electron beam electron-optically.This is also of great importance as it permits to reduce the size of theamplifying stage which will allow to make the apparatus of a smallersize and of a lower cost.

In some applications it is preferable to provide ampli fication of thephoto-electron beam by other means than described above which aretechnologically complicated. FIG. 2 shows a simplified and efficientsolution to the problem of increasing sensitivity of vacuum tube 1 andof the system of Radiography. In this embodiment of invention the film 8is replaced with the composite film 25 which comprises a layer ofdielectric material 26 which when being bombarded by electrons orphoto-electrons produces electrical conductivity changes. Such layer maybe of MgO, alkali halides, ZnS or CdS. Next to layer 26 is layer ofelectrically conducting material 27 which may be of transparent typesuch as Nesa or indium oxide or of nontransparent material such as ofametal like Al or Cu. Next to layer 27 is the supporting layer 28 whichmay be of any flexible material such as of plastics, e.g., polyesters,polyamides, or acetates. The layer 27 is connected to a suitable sourceof electrical potential 29 or to a ground. The rest of vacuum tube lawill have a similar construction as the tube 1 shown in FIG. 1 or in l-Aor in 1-D. The member 40 of electrically conducting material may beconnected to the source of electrical potential or to the ground and maysupport film 25 or may be spaced apart from it. The photo-electron beamfrom the photo-cathode 3 is accelerated to 10-20 KV velocity and when itimpinges on layer 26 it produces therein a pattern of electricalconductivity changes which corresponds to the original X-ray image. Thispattern of electrical conductivity will persist in a suitable materialfor a long time. The film 25 will be now transported to the chargingchamber 3] in which an electrostatic uniform charge will be deposited onthe free surface of layer 26. This charge will leak away due toelectrical conductivity induced in layer 26 and the remaining chargewill have now the pattern of the original X-ray image. Next the film 25is transported into developing chamber 32 in which a suitable toner isapplied to make this charge visible. Next the film 25 is transported tochamber 33 in which it is transferred to another film and after thetransfer it is fixed to produce a permanent image. The new transfermaterial may be preferably of transparent type such as of acetate,polyester, polycarbon or polyamide. The film 25 after cleaning andneutralization of charges will be recycled for the next exposure. Inthis way the new device provides an inexpensive system of radiography inwhich a cheap plastic film will replace expensive X-ray films.

FlG. 2-A shows another embodiment of the film 25 in which only 2 layersare present. The film 35 consists of layer 36 which is of dielectricmaterial such as MgO. alkali halides, ZnS or CdS or Sb S and exhibitselectron bombardment induced conductivity. Next is the layer 37 which isof flexible and electrically conducting material such as copper laminateor other metal laminate and which is made thick enough to beself-supporting. The layer 37 is connected to the source of electricalpotential 29 or to ground. The planar or curved member 40 may be used toprovide support for the film 25 or 35. It may also serve to provide thenecessary curvature for the film 25 or 35 in some cases. It may be alsoconnected to the source of electrical potential to provide highacceleration for the electron beam, such as -20 KV which is necessary toproduce electrical conductivity by electron bombardment. The member 40may be conversely connected to the ground, if the photo-cathode is heldat high negative potential.

In some applications the film or 35 may be precharged with a uniformelectrostatic charge before introducing said film into vacuum tube 1 orits modifications. ln such case its subsequent deposition of electri calcharge after removal of film 25 or 35 from vacuum tube may be omitted.This embodiment of invention is ofimportance if the materials used forfilm 25 or 35 exhibit induced electrical conductivity for a short timeonly. The electron bombardment induced conductivity can produceamplification of the electron beam by the factor of 100 to 1000 andallows therefore to eliminate lother amplification means describedabove, in some applications. In other cases however there may be needfor additional amplification of the electron beam and in such cases theuse may be made of all amplifying devices which were described above. Inparticular, it should be understood that in all devices described abovethe use may be made of amplification of the electron beam either bymeans of another stage composite screen, or of a multi-channel electronmultiplier or of transmission type of electron multiplier such assilicon membrane of p-type. It should be understood that in all devicesdescribed above the focusing means for electron beam may be ofelectrostatic type or of magnetic type or of proximity focusing type.

It should be understood that in all embodiments of invention the finalradiographic image may be made on a transparent substrate or on lightreflecting substrate. It should be understood that in all embodiments ofinvention the final radiograph may be made of either polarity whichmeans that black and white areas of radio graph may be reversedaccording to the need of application. It should be understood that inall embodiments of invention the final radiograph may be produced on theoriginal film which was used in a vacuum tube 1 or its modifications ormay be produced on another film which serves as a transfer medium.

In conclusion, an efficient and inexpensive new system of radiography isprovided by the apparatus described in FIGS. 2 and Z-A and theirmodifications which will provide at the same time better X-rayexaminations and at a much lower cost.

FIG. 3 shows another embodiment of invention which will be useful insome applications. In this em bodiment the vacuum tube 45 comprisesX-ray reactive screen 46 of one of modifications described above and inaddition a composite fluorescent screen 47. Screen 47 comprises lightreflecting layer which is pervious to electrons, e.g., of aluminum 48,fluorescent layer 49 of one of phosphors described above and a lighttranspar ent supporting layer 50 of one of plastics such as polyestersor polyamides or silicones. The layer 50 may also be in the form of afiberoptic member which is constituted of an array of light conductingfibers. Each of said light conducting fibers conducts light by internalreflection and comprises core of transparent material of a high index ofrefraction such as quartz or suitable plastics such as polycarbonates oracrylates. Each of said fibers has a coating of material of a lowerindex of refraction. The coating may be only of a few microns thickness.The plurality of such fibers assembled together forms an array which canconduct the image by internal reflection from one end of said array tothe other end of said array, as it is described in my U.S. Pat. Nos.2,877,368 and 3,021,834. The X-ray image is converted into an electronbeam which represents the orig inal Xray image. This electron beam isdemagnified by electron-optical means and is accelerated to high emergysuch as 20 KV to excite the fluorescent layer 49 and to producefluorescent image corresponding to X-ray image. The fluroescent image isconducted by the supporting member 50 and irradiates the imagereproducing film 55. In some cases the electron beam is not demagnifiedbut is of original size. This is the case when proximity focusing isused.

The image reproducing film 55 has different construction from the film25 or 35 because the first layer which receives the fluorescent image isthe layer 56 which is of dielectric material and which has alsophoto-conductive properties. Such materials are Se, Zns and CdS and Sb Swith suitable activators such as As or Te. The next layer 57 iselectrically conducting material and may be of light transparent typesuch as Nesa or indium oxide or of light non-transparent material suchas a metal. The next layer 58 is a supporting member which is offlexible and dielectric material and which may be of light transparenttype or of light impervious type. Materials such as plastics describedabove or fiber glass or laminates of glass may be used for layer 58. Thefilm 55 may be also simplified to consist of two layers only. In thisembodiment the electrically conducting layer 57 is made thick enough toserve as a supporting layer and is constructed to be flexible. It may betherefore made of laminates of metals such as copper or other metalswhich provides the necessary flexibility. The electrically conductinglayer 57 may be connected to the source of electrical potential or toground. The film 55 is mounted in a very close spacing to the supportingmember 50 such as not exceeding lOO microns. In cases in which thesupporting member 50 is made of fiberoptic plate described above, film55 may be in contact with the member 50. The supporting member 50 may beof planar shape or of curved shape according to the electron-opticalsystem used. In cases in which the supporting member 50 is of plasticthe film 55 may be self-supporting or may rest on the support in theform of separate member 40 as was shown in FIGS. 1 and 2. Thephotoconductive layer 56 of film 55 when exposed to the fluorescentimage from the layer 49 responds with changes of its electricalconductivity which have the pattern of said fluorescent image. Thisphoto conductivity pattern will persist in a photo-conductor material ofstorage type for a long time. Materials such as Sb S with activatorssuch as As and Te have very good storage properties. The film 55 may benow transported through vacuum safety locks 17 to the outside of vacuumtube 45 into charging chamber 31 in which it receives a uniformelectrostatic charge as described above. The electrostatic charge leaksaway through the areas which were made electrically conductive byfluorescent image. The remaining charge will be the replica of theoriginal fluorescent image. The film 55 is now transported to thedeveloping chamber 32 in which a toner in the form of one of blackpowders is applied to visualize the pattern of electrostatic charges.Next the film 55 is transported to the transfer chamber 33 where theelectrostatic charge with toner is transferred to the final supportingsheet which may be oflight transparent or light impervious material andis fixed therein as was described above.

It should be understood in all devices described above, the X-rayreactive photocathode 3 may be of composite screen type described aboveand illustrated in FIGS. 1 or 1A; or may be of a metal 3a of high atomicnumber such as tungsten or lead as illustrated in FIG. 1B; or may be ofa neutron-sensitive type as described in my U.S. Pat. No. 2,555,423.

It should be understood that in all devices described above the use maybe made of amplification ofthe electron beam either by means of anotherstage composite screen, or of a multi-channel electron multiplier or oftransmission type of electron multiplier such as silicon membrane ofp-type. It should be understood that in all devices described above thefocusing means for electron beam may be of electrostatic type or ofmagnetic type or of proximity focusing type. It should be understoodthat an ion pump is intended to be used in all embodiments of inventionfor the best gettering action.

It should be understood that dielectric material described above mans amaterial which has electrical resistivity not less than ohm-cm. Itshould be under stood that in all embodiments of invention said meansfor receiving electron beam may be informed of a sheet or tape and maybe flexible, semi-flexible or non-flexible.

It should be understood that in all embodiments of invention the finalradiographic image may be made on a transparent substrate or on lightreflecting substrate. It should be understood that in all embodiments ofinvention the final radiograph may be made of either polarity, whichmeans black and white areas of radio graph may be reversed according tothe need of appli 8 cation. It should be understood that in allembodiments of invention the final radiograph may be produced on theoriginal film which was used in a vacuum tube or may be produced onanother medium which serves as a transfer medium.

It should be understood that the particular embodiments and forms ofthis invention have been illustrated and it is understood thatmodifications may be made by those skilled in the art without departingfrom the scope and spirit of the foregoing disclosure.

What I claim is:

1. An apparatus for medical radiography for X-ray examination of humanbody comprising in combination a vacuum tube comprising an X rayreactive screen producing in response to an X-ray image a beam ofelectrons corresponding to said image, image storage means receivingsaid beam of electrons and intensifying said beam, said image storagemeans comprising a layer of material exhibiting electron bombardmentinduced conductivity and an electrically conducting member, said imagestorage means being movable from the outside of said tube into said tubeand movable from said tube to the outside of said tube, said vacuum tubecomprising in addition vacuum safety locks for protecting vacuum of saidtube during removal of said image storage means from said tube. andmeans for converting said stored and intensified image moved outside ofsaid vacuum tube into a visible image for inspection.

2. A device as defined in claim 1 in which said electrically conductingmember is connected to a source of electrical potential mounted outsideof said vacuum tube.

3. A device as defined in claim I in which said image storage means areflexible.

4. A device as defined in claim 1 in which the whole of said stored andintensified image is converted simultaneously into a visible image.

5. A device as defined in claim 2 in which said image storage means areflexible.

6. A device as defined in claim 2 in which the whole of said stored andintensified image is converted simultaneously into a visible image.

7. A vacuum tube for medical radiography of human body comprising incombination an X-ray reactive screen producing in response to an X-rayimage a beam of electrons corresponding to said image, image storagemeans receiving said beam of electrons, and intensifying said beam, saidimage storage means comprising a layer of material exhibiting electronbombardment induced conductivity and an electrically conducting member,said image storage means being movable from the outside of said tubeinto said tube and movable from said tube to the outside of said tube,said vacuum tube comprising furthermore vacuum safety iocks protectingthe vacuum of said tube during removal of said image storage means fromsaid tube.

8. A device as defined in claim 7 in which said electrically conductingmember is connected to a source of electrical potential mounted outsideof said vacuum tube.

9. A device as defined in claim 7 in which said image storage means areflexible.

* i l i

1. An apparatus for medical radiography for X-ray examination of humanbody comprising in combination a vacuum tube comprising an X-rayreactive screen producing in response to an X-ray image a beam ofelectrons corresponding to said image, image storage means receivingsaid beam of electrons and intensifying said beam, said image storagemeans comprising a layer of material exhibiting electron bombardmentinduced conductivity and an electrically conducting member, said imagestorage means being movable from the outside of said tube into said tubeand movable from said tube to the outside of said tube, said vacuum tubecomprising in addition vacuum safety locks for protecting vacuum of saidtube during removal of said image storage means from said tube, andmeans for converting said stored and intensified image moved outside ofsaid vacuum tube into a visible image for inspection.
 2. A device asdefined in claim 1 in which said electrically conducting member isconnected to a source of electrical potential mounted outside of saidvacuum tube.
 3. A device as defined in claim 1 in wHich said imagestorage means are flexible.
 4. A device as defined in claim 1 in whichthe whole of said stored and intensified image is convertedsimultaneously into a visible image.
 5. A device as defined in claim 2in which said image storage means are flexible.
 6. A device as definedin claim 2 in which the whole of said stored and intensified image isconverted simultaneously into a visible image.
 7. A vacuum tube formedical radiography of human body comprising in combination an X-rayreactive screen producing in response to an X-ray image a beam ofelectrons corresponding to said image, image storage means receivingsaid beam of electrons, and intensifying said beam, said image storagemeans comprising a layer of material exhibiting electron bombardmentinduced conductivity and an electrically conducting member, said imagestorage means being movable from the outside of said tube into said tubeand movable from said tube to the outside of said tube, said vacuum tubecomprising furthermore vacuum safety locks protecting the vacuum of saidtube during removal of said image storage means from said tube.
 8. Adevice as defined in claim 7 in which said electrically conductingmember is connected to a source of electrical potential mounted outsideof said vacuum tube.
 9. A device as defined in claim 7 in which saidimage storage means are flexible.